Yes there still exist worthwhile fonts that exist in METAFONT format and are not already available in OTF.
A couple of examples are the Devanagari (Sanskrit) fonts by Velthuis and Wikner: see this answer for details on what these fonts are, and what has been done already. The interesting addition here would be to remap the glyphs from the font to their Unicode points, and to set up GSUB rules, etc. This would be worthwhile to do, as there is still some interest in using those fonts. I think there exist other similar examples of Non-Latin fonts (for example the fonts inside
bengali, in the directory mentioned below).
More generally, you can look inside the
/texmf-dist/fonts/source/public directory in a TeX Live distribution. (One from many years ago is here.) Or even go one level higher…
One interesting font that is of historical interest would have been the Punk METAFONT, which Knuth wrote about in TUGboat, after creating it in a single afternoon:
At 1 p.m. I went to the computer and began to compose a simple base file. […] by 4 p.m. I was ready to make the first trial setting of text
But it looks like this has already been converted to OTF by Khaled Hosny; see the
punknova package on CTAN or his
punk-otf GitHub repo.